Distinguishing tautomerism in the crystal structure of (Z)-N-(5-ethyl-2,3-dihydro-1,3,4-thiadiazol-2-ylidene)-4-methylbenzenesulfonamide using DFT-D calculations and¹³C solid-state NMR

Abstract

The crystal structure of (Z)-N-(5-ethyl-2,3-di­hydro-1,3,4-thia­diazol-2-yl­idene)-4-methyl­benzene­sulfonamide contains an imine tautomer, rather than the previously reported amine tautomer. The tautomers can be distinguished using dispersion-corrected density functional theory calculations and by comparison of calculated and measured 13C solid-state NMR spectra.

The application of tailor-made force fields and molecular dynamics for NMR crystallography: a case study of free base cocaine

“…The performance of a TMFF for free base cocaine for the motional averaging aspects of ab initio 13 C and 1 H isotropic NMR chemical shift calculations is assessed and compared with existing benchmarks, including static PBE-D2 energy minimizations (Li et al, 2014), motional averaging with the COMPASS force field (Li et al, 2016) and the literature (Baias, Widdifield et al, 2013). In general, the TMFF gives an accurate representation for the motional averaging of CSP candidates, but this does not give a significant improvement in the accuracy of SS-NMR calculations.…”

“…Thus, to keep the consistency of the protocols we used for two of our previous studies (Li et al, 2014(Li et al, , 2016, the semi-empirical type Grimme-2006 dispersioncorrection scheme (Grimme, 2006) with the PBE functional was used, referred to as PBE-D2. The protocol for the energy minimizations was described by Li et al (2014) with one exception in this particular case: energy minimizations with only the hydrogen atoms allowed to move were omitted, because all the crystal structure candidates were generated from PBE-D3 calculations; the positions of the hydrogen atoms are, in most cases, more accurate than the experimental X-ray diffraction data. The convergence criteria for the energy minimizations were: change in the total energy 9.649 Â 10 À4 kJ mol À1 , maximum force 2.895 kJ mol À1 Å À1 , maximum stress tolerance 0.05 GPa, maximum atomic displacement 0.003 Å .…”

“…Density functional theory (DFT)-based methods are widely used in NMR crystallography. For example, dispersion-corrected DFT (DFT-D), which is a popular and practical method that provides a compromise between accuracy and speed to reproduce the packings and energies of molecular crystals (Day et al, 2009;Bardwell et al, 2011;Reilly et al, 2016), is used extensively for geometry optimizations (Dudenko et al, 2013;Li et al, 2014;Hartman & Beran, 2014;Sneddon et al, 2014;Widdifield et al, 2016;Watts et al, 2016;Gumbert et al, 2016;Folliet et al, 2013), and the gauge-including projector augmented wave (GIPAW) method (Pickard & Mauri, 2001) is used to calculate magnetic shieldings for periodic systems.…”

A comparative study of the crystal structures of 2-(4-(2-(4-(3-chlorophenyl)pipera -zinyl)ethyl) benzyl)isoindoline-1,3-dione by synchrotron radiation X-ray powder diffraction and single-crystal X-ray diffraction

“…Despite having a variety of known functions, the crystal structure of the title compound, 2-(4-(2-(4-(3-chlorophenyl)-piperazin-1-yl)ethyl)benzyl) iso -indoline-1,3-dione, was still unknown. Therefore, in this paper, we presented the crystal structure of compound 1 that were analyzed by both single-crystal X-ray diffraction (SXRD) and synchrotron radiation X-ray powder diffraction (PXRD), while the powder diffraction data were solved by the simulated annealing method and was further verified by rigid-body Rietveld refinement, and the single-crystal diffraction data were solved by direct methods and refined with full-matrix least-squares techniques [13][14][15][16]. Very little work had been done in comparing the crystal structure data, such as bond length and bond angle, obtained from these two approaches.Li and his co-workers reported a comparative study of the crystal structure data of griseofulvin obtained from SXRD and PXRD [17].…”

An NMR crystallography investigation of furosemide

“…Solid‐state NMR, being a sensitive local probe, has a complementary nature to pXRD that relies on long‐range order. With first‐principles GIPAW calculations tying these two techniques together, NMR crystallography has a proven track record in analysing and validating solid structures …”